We report a record-size, two-dimensional polariton condensate of a fraction of a millimeter radius free from the presence of an exciton reservoir. This macroscopically occupied state is formed by the ballistically expanding polariton flow that relaxes and condenses over a large area outside of the excitation spot. The density of this trap-free condensate is < 1 polariton/{\mu}m^2, reducing the phase noise induced by the interaction energy. Moreover, the backflow effect, recently predicted for the nonparabolic polariton dispersion, is observed here for the first time in the fast-expanding wave packet.
@article{arxiv.1609.05717,
title = {Macroscopic Two-Dimensional Polariton Condensates},
author = {Dario Ballarini and Davide Caputo and Carlos Sánchez Muñoz and Milena De Giorgi and Lorenzo Dominici and Marzena H. Szymańska and Kenneth West and Loren N. Pfeiffer and Giuseppe Gigli and Fabrice P. Laussy and Daniele Sanvitto},
journal= {arXiv preprint arXiv:1609.05717},
year = {2021}
}